Influence of systolic intracavity pressure on right ventricular perfusion in the awake dog

This study tested the hypothesis that an acute increase in right ventricular pressure would result in selective impedance of blood flow into the right ventricular subendocardium (ENDO) similar to that seen normally in the left ventricle. Since tachycardia (reduces diastolic time) and vasomotor paralysis will reveal impedence to blood flow by a decrease in ENDO to subepicardial (EPI) myocardial blood flow (MBF) ratio, MBF was measured with microspheres in eight awake dogs during rapid pacing at 176 +/- 2 beats . min-1 (mean +/- SE) after acute pulmonary artery constriction (PAC) before and during adenosine (A) infusion (1.00 mg . kg-1 . min-1). AP was held constant by aortic constriction. During control pacing the ENDO/EPI ratios were 1.38 +/- 0.08 and 1.46 +/- 0.12 in the RV and LV, respectively. During adenosine infusion the ENDO/EPI decreased to 0.85 +/- 0.08 (P less than 0.05) in the LV but did not change in the RV (1.17 +/- 0.10). During PAC and pacing alone the RV ENDO/EPI was 1.24 +/- 0.05 (NS vs control), but during adenosine fell to 0.88 +/- 0.07 (P less than 0.05). Transmural blood flow to the interventricular septum (IVS) was also affected by increased RV pressure. During control the ratio of blood flow to the left and right side (LV/RV) of the IVS was 1.32 +/- 0.12. PAC alone caused a redistribution of MBF toward the right side and the LV/RV fell to 0.66 +/- 0.06 (P less than 0.05). During PAC and adenosine, however the LV/RV rose to 1.38 +/- 0.08. These data demonstrate that increased RV systolic pressure produces systolic impedance to blood flow to the right ventricular ENDO and the right side of the interventricular septum.